1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of preventing poor alignment caused by a column spacer to improve a contrast ratio.
2. Description of the Related Art
In general, a liquid crystal display (LCD) device controls the light transmittance of liquid crystal cells in response to video signals to thereby display pictures corresponding to the video signals on a liquid crystal display panel. To this end, the LCD device includes a liquid crystal display panel having liquid crystal cells arranged in an active matrix form, and driving circuits for driving the liquid crystal display panel.
Depending on a direction of an electric field driving a liquid crystal material, the LCD device is generally classified into two modes—a twisted nematic (TN) mode using a vertical electric field and an in-plane switching (IPS) mode using a horizontal electric field.
The TN mode LCD device drives the liquid crystal material using a vertical electric field formed between a common electrode and an opposing pixel electrode. The TN mode LCD device has high aperture ratios, but narrow viewing angles. The IPS mode LCD device drives the liquid crystal material using a horizontal electric field formed between the pixel electrode and the common electrode located in parallel on one substrate. The IPS mode LCD device has wide viewing angles, but low aperture ratios.
FIG. 1 is a plan view illustrating a related art IPS mode liquid crystal display panel.
Referring to FIG. 1, the IPS mode liquid crystal display panel includes: a color filter array substrate having a black matrix, a color filter, a planarization layer, a column spacer 13, and an upper alignment layer, which are sequentially formed on an upper substrate whose rear surface is covered with materials (not shown) for a transparent electrode for preventing static electricity; a thin film transistor array substrate having a thin film transistor (TFT), a common electrode, a pixel electrode, and a lower alignment layer, all of which are formed on a lower substrate; and a liquid crystal material (not shown) injected in the inner space between the color array substrate and the thin film transistor array substrate.
The column spacer 13 is regularly formed at a defined location on a red sub-pixel R region within one pixel having red, green and blue sub-pixels to serve to maintain a cell gap between the color filter array substrate and the thin film transistor array substrate. Also, the column spacer 13 may be regularly formed at a defined location on a green sub-pixel G region within one pixel and may be regularly formed at a defined location on a blue sub-pixel B region within one pixel.
Meanwhile, a rubbing process is performed on the upper and the lower alignment films in order to control initial alignment of the liquid crystal disposed therebetween. In the rubbing process, a rubbing roller rolls up a rubbing material. The surface of the alignment film is rubbed using the rubbing roller with the rubbing material in a direction defined from upward to downward such as in a direction parallel to an alignment direction A of the column spacer 13 as shown in FIG. 2.
However, if the rubbing process is performed, then the rubbing material passes by the column spacer 13 regularly formed on the defined location, to thereby cause sectional damage at a particular portion of the rubbing material.
In other words, a rubbing scratch S, representing uneven alignment concentrated along the column spacer 13 arranged in a line as shown in FIG. 2, occurs, to thereby generate light leakage. As a result, a black brightness is increased, to thereby deteriorate the contrast ratio.
Meanwhile, in order to prevent the sectional damage in the rubbing material, as shown in FIG. 3, there has been proposed a structure, in which the column spacer 13 is formed within the other sub-pixels in one pixel. However, the red, green and blue color filters have different thicknesses due to process deviations. Accordingly, the cell gap is uneven.